Polymer and organic electronic device

ABSTRACT

A composition comprising a polymer and a phosphorescent material wherein the polymer comprises repeat units of formula (I): 
                         
wherein A is a heteroaryl group containing a nitrogen atom, and A may be unusubstituted or substituted with one or more substituents;
     R 1  in each occurrence is independently a substituent; and   n is 0, 1, 2, 3 or 4.

RELATED APPLICATION

This application claims priority to United Kingdom Patent Application No.: 1223083.1, filed on Dec. 21, 2012 , the entirety of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Electronic devices containing active organic materials are attracting increasing attention for use in devices such as organic light emitting diodes (OLEDs), organic photoresponsive devices (in particular organic photovoltaic devices and organic photosensors), organic transistors and memory array devices. Devices containing active organic materials offer benefits such as low weight, low power consumption and flexibility. Moreover, use of soluble organic materials allows use of solution processing in device manufacture, for example inkjet printing or spin-coating.

An OLED may comprise a substrate carrying an anode, a cathode and one or more organic light-emitting layers between the anode and cathode.

Holes are injected into the device through the anode and electrons are injected through the cathode during operation of the device. Holes in the highest occupied molecular orbital (HOMO) and electrons in the lowest unoccupied molecular orbital (LUMO) of a light-emitting material combine to form an exciton that releases its energy as light.

A light emitting layer may comprise a semiconducting host material and a light-emitting dopant wherein energy is transferred from the host material to the light-emitting dopant. For example, J. Appl. Phys. 65, 3610, 1989 discloses a host material doped with a fluorescent light-emitting dopant (that is, a light-emitting material in which light is emitted via decay of a singlet exciton).

Phosphorescent dopants are also known (that is, a light-emitting dopant in which light is emitted via decay of a triplet exciton).

A hole-transporting layer may be provided between the anode and light-emitting layer of an OLED.

Suitable light-emitting materials include small molecule, polymeric and dendrimeric materials. Suitable light-emitting polymers include poly(arylene vinylenes) such as poly(p-phenylene vinylenes) and polymers containing arylene repeat units, such as fluorene repeat units. Blue light-emitting fluorene homopolymer is disclosed in WO 97/05184.

WO 2010/085676 discloses host materials for electrophosphorescent devices. A copolymer formed by copolymerization of 1,6-bis(3-(4,4,5,5-tetramethyl-[1,3,2]-dioxaborolan-2-yl)phenoxyl)hexane and 2-(4-(3-(3,6-dibromocarbazol-9-yl)propyl)phenyl)-4,6-di(3-methylphenyl)-1,3,5-triazine is disclosed.

WO 2008/025997 discloses the following monomer for use in preparation of a polymeric host:

WO 2010/136109 discloses the following intermediate compound:

Dibenzosilole polymers and applications in organic electronics are disclosed in Journal of Material Chemistry (2011), 21(32), 11800-11814.

Gaofenzi Xuebao (2009), (11), 1120-1125 discloses a polymer comprising the following monomers:

SUMMARY OF THE INVENTION

In a first aspect the invention provides a composition comprising a polymer and a phosphorescent material wherein the polymer comprises repeat units of formula (I):

wherein A is a heteroaryl group containing a nitrogen atom, and A may be unusubstituted or substituted with one or more substituents;

-   R¹ in each occurrence is independently a substituent; and -   n is 0, 1, 2, 3 or 4.

In a second aspect the invention provides a formulation comprising a composition according to the first aspect and at least one solvent.

In a third aspect the invention provides an organic light-emitting device comprising an anode, a cathode and a light-emitting layer between the anode and cathode wherein the light-emitting layer comprises a composition according to the first aspect.

In a fourth aspect the invention provides a method of forming an organic light-emitting device according to the third aspect comprising the step of forming the light-emitting layer over one of the anode and the cathode and forming the other of the anode and the cathode over the light-emitting layer.

Optionally according to the fourth aspect, the light-emitting layer is formed by depositing a formulation according to the third aspect and evaporating the at least one solvent.

In a fifth aspect the invention provides a polymer comprising a repeat unit of formula (III):

wherein:

-   R² is H or a substituent; -   R¹ in each occurrence is independently a substituent; and -   n is 0, 1, 2, 3 or 4.

Optionally according to the fifth aspect R² is an aromatic ring or a branched or linear chain of aromatic rings, wherein each ring may be unsubstituted or substituted with one or more substituents R⁴.

Optionally according to the fifth aspect R² is phenyl.

Optionally according to the fifth aspect each R⁴ is independently selected from the group consisting of C₁₋₂₀ alkyl wherein one or more non-adjacent C atoms of the C₁₋₂₀ alkyl may be replaced with O or S and one or more H atoms of the C₁₋₂₀ alkyl may be replaced with F.

In a sixth aspect the invention provides a method of forming a polymer comprising the step of polymerising a monomer of formula (IV):

wherein LG is a leaving group capable of leaving in a coupling reaction to form a carbon-carbon bond with an aromatic or heteroaromatic group, and wherein R¹, R² and n are as described with reference to any preceding aspect.

In a seventh aspect the invention provides a formulation comprising a polymer according to the fifth aspect and at least one solvent.

In an eighth aspect the invention provides an organic light-emitting device comprising an anode, a cathode and a light-emitting layer between the anode and cathode wherein the light-emitting layer comprises a polymer according to the fifth aspect.

In a ninth aspect the invention provides a method of forming an organic light-emitting device according to the eighth aspect comprising the step of forming the light-emitting layer over one of the anode and the cathode and forming the other of the anode and the cathode over the light-emitting layer.

Optionally according to the ninth aspect the light-emitting layer is formed by depositing a formulation according to the seventh aspect and evaporating the at least one solvent.

DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail with reference to the drawings in which:

FIG. 1 illustrates schematically an OLED according to an embodiment of the invention; and

FIG. 2 shows the photostability of a host polymer material according to an embodiment of the invention and a comparative host polymer material.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates an OLED 100 according to an embodiment of the invention comprising an anode 101, a cathode 105 and a light-emitting layer 103 between the anode and cathode. The device 100 is supported on a substrate 107, for example a glass or plastic substrate.

One or more further layers may be provided between the anode 101 and cathode 105, for example hole-transporting layers, electron transporting layers, hole blocking layers and electron blocking layers. The device may contain more than one light-emitting layer.

Preferred device structures include:

Anode/Hole-injection layer/Light-emitting layer/Cathode

Anode/Hole transporting layer/Light-emitting layer/Cathode

Anode/Hole-injection layer/Hole-transporting layer/Light-emitting layer/Cathode

Anode/Hole-injection layer/Hole-transporting layer/Light-emitting layer/Electron-transporting layer/Cathode.

Preferably, at least one of a hole-transporting layer and hole injection layer is present.

Preferably, both a hole injection layer and hole-transporting layer are present.

Light-emitting materials include red, green and blue light-emitting materials.

A blue emitting material may have a photoluminescent spectrum with a peak in the range of no more than 490 nm, optionally in the range of 420-480 nm.

A green emitting material may have a photoluminescent spectrum with a peak in the range of more than 490 nm up to 580 nm, optionally more than 490 nm up to 540 nm.

A red emitting material may optionally have a peak in its photoluminescent spectrum of more than 580 nm up to 630 nm, optionally 585-625 nm.

Light-emitting layer 103 contains a polymer of the invention and one or more phosphorescent materials, to form a host-dopant system. The light-emitting layer 103 may consist essentially of these materials or may contain one or more further materials, for example one or more charge-transporting materials or one or more further light-emitting materials. The triplet energy level of the host polymer is preferably no more than 0.1 eV below that of the light-emitting material, and is more preferably about the same or higher than that of the light-emitting material in order to avoid quenching of phosphorescence from the light-emitting dopant. Optionally, the lowest triplet energy level of the host polymer is at least at least 2.4 or at least 2.6 eV. The triplet energy level of the host polymer may be selected according to the shortest wavelength phosphorescent material used with the host. For example, if a green phosphorescent material is the shortest wavelength material then the triplet energy level of the host material may be lower than that of a host for a blue phosphorescent material.

In a preferred embodiment, light-emitting layer 103 contains a composition and a polymer of the invention and at least one of green and blue phosphorescent light-emitting materials.

If present, a charge-transporting layer adjacent to a phosphorescent light-emitting layer preferably contains a charge-transporting material having a T₁ excited state energy level that is no more than 0.1 eV lower than, preferably the same as or higher than, the T₁ excited state energy level of the phosphorescent light-emitting material(s) of the invention in order to avoid quenching of triplet excitons migrating from the light-emitting layer into the charge-transporting layer.

Triplet energy levels may be measured from the energy onset of the phosphorescence spectrum measured by low temperature phosphorescence spectroscopy (Y. V. Romaovskii et al, Physical Review Letters, 2000, 85 (5), p 1027 , A. van Dijken et al, Journal of the American Chemical Society, 2004, 126 , p 7718).

In a first aspect, the invention provides a composition comprising a polymer and a phosphorescent material wherein the polymer comprises repeat units of formula (I):

wherein A is a heteroaryl group containing a nitrogen atom, and wherein A may be unusubstituted or substituted with one or more substituents;

-   R¹ in each occurrence is independently a substituent; and -   n is 0, 1, 2, 3 or 4.

A may be selected from the group consisting of triazine, pyrimidine, pyridine, triazole and oxadiazole.

A may be substituted with at least one substituent R².

Each R² may independently be a C₁₋₄₀ hydrocarbyl.

Exemplary C₁₋₄₀ hydrocarbyl groups include alkyl; aryl, preferably phenyl; or a linear or branched chain of aryl groups, preferably a linear or branched chain of phenyl groups, that may be unsubstituted or substituted with one or more substituents. Exemplary hydrocarbyl substituents include the following:

-   -   C₁₋₂₀ alkyl     -   Phenyl substituted with one or more C₁₋₂₀ alkyl groups     -   A branched or linear chain of two or more phenyl rings, each of         which ring may be substituted with one or more C₁₋₂₀ alkyl         groups, for example biphenyl or 3,5-diphenylbenzene.

Exemplary aromatic hydrocarbyl groups include the following, each of which may be substituted with one or more substituents:

Exemplary groups R¹ include C₁₋₄₀ hydrocarbyl, —OR¹¹, —SR¹¹, —NR¹¹ ₂, and —SiR¹¹ ₃, wherein R¹¹ in each occurrence is a substituent, preferably C₁₋₄₀ hydrocarbyl.

Exemplary hydrocarbyl groups R¹ and R¹¹ include C₁₋₂₀ alkyl; unsubstituted phenyl; phenyl substituted with one or more C₁₋₂₀ alkyl groups; and a branched or linear chain of phenyl groups wherein each phenyl is unsubstituted or substituted with one or more C₁₋₂₀ alkyl groups. C₁₋₂₀ alkyl is preferred.

One or more non-adjacent C atoms of R¹ and, where present, R² may independently be replaced with —O—, —S—, —NR¹¹—, —SiR¹¹ ₂—, C(═O) or —COO—.

Optionally, R² is a C₁₂₋₄₀ hydrocarbyl group containing two or more aryl groups, preferably two or more phenyl groups.

Alkyl groups as described anywhere herein includes linear, branched and cyclic alkyl groups. In the case of R², a C₃₋₂₀ branched alkyl group, including alkyl groups containing one or more C atoms selected from secondary and tertiary carbon atoms, may provide more steric hindrance and therefore a greater degree of twisting than a corresponding linear alkyl group.

In one embodiment the repeat unit of formula (I) has formula (Ia):

wherein:

-   X in each occurrence is independently selected from N and CR¹²     wherein R¹² in each occurrence is independently H or a substituent,     with the proviso that at least one X is N, -   R² is a substituent as described above; and m is 0 or 1.

Each X of the repeat unit of formula (Ia) is preferably N.

Each R¹² is preferably selected from H and C₁₋₂₀ alkyl.

Exemplary repeat units of formula (I) are shown below, wherein R and R′ in each occurrence is H or a substituent, preferably a C₁₋₂₀ alkyl.

The extent of conjugation of the substituent R² may affect the triplet energy level of the polymer. In the case where R² contains a chain of phenyl groups, para linkage between phenyl groups may result in a greater degree of conjugation than meta-linkage. In one embodiment, R² is a phenyl group wherein one or both meta-positions of the phenyl group are substituted with an unsubstituted or substituted aryl or heteroaryl group, preferably a phenyl group that may be unsubstituted or substituted with one or more C₁₋₂₀ alkyl groups.

In the case where R2 is a phenyl group that is further substituted with one or more aryl or heteroaryl groups, a substituent may be provided ortho- to the aryl or heteroaryl substituent or substituents to create a twist between the phenyl and the aryl or heteroaryl substituents. In one embodiment, R2 is a phenyl group having one or two phenyl meta-substituents, and a 4-substituent to create a twist between the phenyl group and the phenyl meta-substituents. Optionally, the 4-substituent is selected from C₁₋₂₀ alkyl.

In one embodiment the polymer of the composition of the invention is a copolymer having a repeat unit of formula (I) and one or more co-repeat units.

Exemplary co-repeat units include arylene co-repeat units that may be unsubstituted or substituted with one or more substituents. A preferred arylene co-repeat unit is a phenylene repeat unit that may be unsubstituted or substituted with one or more substituents.

In one preferred arrangement the one or more co-repeat units include a conjugation-breaking repeat unit, which is a repeat unit that does not provide any conjugation path between repeat units adjacent to the conjugation-breaking repeat unit.

Exemplary conjugation-breaking co-repeat units include co-repeat units of formula (II):

wherein:

-   Ar¹ in each occurrence independently represents an aryl or     heteroaryl group that may be unsubstituted or substituted with one     or more substituents; and -   Sp represents a spacer group comprising at least one carbon or     silicon atom.

Preferably Ar¹ is an aryl group and the Ar¹ groups may be the same or different, more preferably each Ar¹ is phenyl.

Optionally, each Ar¹ is unsubstituted or substituted with one or more C₁₋₄₀ hydrocarbyl groups as described above with reference to R², which may be the same or different in each occurrence.

Exemplary groups Sp include a C₁₋₂₀ alkyl chain wherein one or more non-adjacent C atoms of the chain may be replaced with O, S, —NR¹¹-, —SiR¹¹ ₂-, —C(═O)— or —COO— and wherein R¹¹ in each occurrence is as described above.

The phosphorescent material of the composition according to the invention is preferably a metal complex.

In one arrangement the phosphorescent material of the composition according to the invention is mixed with the polymer.

In another arrangement the phosphorescent material of the composition according to the invention is covalently bound to the polymer. In this arrangement, the phosphorescent material may be provided as a main-chain repeat unit of the polymer backbone, an end-group of the polymer or a side-group of the polymer that may be directly bound to the polymer backbone or spaced apart from the polymer backbone by a spacer group, for example a C₁₋₂₀ alkyl group.

Optionally, a photoluminescence spectrum of the phosphorescent material has a peak at a wavelength no more than 490 nm, optionally in the range of 420-575 nm, more preferably 420-480 nm.

In a further aspect the invention provides a formulation comprising a composition according to the first aspect of the invention and at least one solvent.

In another aspect, the invention provides an organic light-emitting device comprising an anode, a cathode and a light-emitting layer between the anode and cathode wherein the light-emitting layer comprises a composition according to the first aspect of the invention.

The invention also provides a method of forming an organic light-emitting device according to the invention, comprising the step of forming the light-emitting layer over one of the anode and the cathode and forming the other of the anode and the cathode over the light-emitting layer.

Optionally, the light-emitting layer is formed by depositing a formulation according to the invention and evaporating the at least one solvent.

In yet another aspect, the invention provides a polymer comprising a repeat unit of formula (III):

wherein:

-   R² is H or a substituent; -   R¹ in each occurrence is independently a substituent; and -   n is 0, 1, 2, 3 or 4.

In one arrangement R² is an aromatic group that may be unsubstituted or substituted with one or more sub stituents R⁴.

Preferably R² is phenyl that may be unsubstituted or substituted with one or more substituents.

Optionally each R⁴, where present, is independently selected from the group consisting of C₁₋₂₀ alkyl, wherein one or more non-adjacent C atoms of the C₁₋₂₀ alkyl may be replaced with O or S and one or more H atoms of the C₁₋₂₀ alkyl may be replaced with F.

The invention further provides a method of forming the polymer comprising a repeat unit of formula (III), the method comprising the step of polymerising a monomer of formula (IV):

wherein each LG is independently a leaving group capable of leaving in a coupling reaction to form a carbon-carbon bond with an aromatic or heteroaromatic group, and

-   R¹, R² and n are as described above.

Each LG is independently selected from the group consisting of halogens, preferably bromine or iodine; boronic acids; boronic esters; sulfonic acids; and sulfonic esters.

Optionally the polymerisation is carried out in the presence of a metal catalyst.

The invention also provides a formulation and an organic light emitting device comprising a polymer comprising a repeat unit of formula (III) and a method of forming the organic light emitting device.

Polymers as described herein suitably have a polystyrene-equivalent number-average molecular weight (Mn) measured by gel permeation chromatography in the range of about 1×10³ to 1×10⁸, and preferably 1×10³ to 5×10⁶. The polystyrene-equivalent weight-average molecular weight (Mw) of the polymers described herein may be 1×10³ to 1×10⁸, and preferably 1×10⁴ to 1×10⁷.

Polymers described herein are suitably amorphous polymers.

Polymer Synthesis

One method of forming conjugated or partially conjugated polymers is Suzuki polymerisation, for example as described in WO 00/53656 or U.S. Pat. No. 5,777,070 which allows formation of C—C bonds between two aromatic or heteroaromatic groups, and so enables formation of polymers having conjugation extending across two or more repeat units. Suzuki polymerisation takes place in the presence of a palladium complex catalyst and a base.

As illustrated in Scheme 1 , in the Suzuki polymerisation process a monomer for forming repeat units RU1 having leaving groups LG1 such as boronic acid or boronic ester groups undergoes polymerisation with a monomer for forming repeat units RU2 having leaving groups LG2 such as halogen, sulfonic acid or sulfonic ester to form a carbon-carbon bond between Arylene 1 and Arylene 2: nLG1-RU1-LG1+nLG2-RU2-LG2→—(RU1-RU2)_(n)- Scheme 1

Exemplary boronic esters have formula (V):

wherein R⁶ in each occurrence is independently a C₁₋₂₀ alkyl group, * represents the point of attachment of the boronic ester to an aromatic ring of the monomer, and the two groups R⁶ may be linked to form a ring. In a preferred embodiment, the two groups R⁶ are linked to form the pinacol ester of boronic acid:

It will be understood by the skilled person that a monomer LG1-RU1-LG1 will not polymerise to form a direct carbon-carbon bond with another monomer LG1-RU1-LG1. A monomer LG2-RU2-LG2 will not polymerise to form a direct carbon-carbon bond with another monomer LG2-RU2-LG2.

Preferably, one of LG1 and LG2 is bromine or iodine and the other is a boronic acid or boronic ester.

This selectivity means that the ordering of repeat units in the polymer backbone can be controlled such that all or substantially all RU1 repeat units formed by polymerisation of LG1-RU1-LG1 are adjacent, on both sides, to RU2 repeat units.

In the example of Scheme 1 above, an AB copolymer is formed by copolymerisation of two monomers in a 1:1 ratio, however it will be appreciated that more than two or more than two monomers may be used in the polymerisation, and any ratio of monomers may be used.

The base may be an organic or inorganic base. Exemplary organic bases include tetra-alkylammonium hydroxides, carbonates and bicarbonates. Exemplary inorganic bases include metal (for example alkali or alkali earth) hydroxides, carbonates and bicarbonates.

The palladium complex catalyst may be a palladium (0) or palladium (II) compound.

Particularly preferred catalysts are tetrakis(triphenylphosphine)palladium (0) and palladium (II) acetate mixed with a phosphine.

A phosphine may be provided, either as a ligand of the palladium compound catalyst or as a separate compound added to the polymerisation mixture. Exemplary phosphines include triarylphosphines, for example triphenylphosphines wherein each phenyl may independently be unsubstituted or substituted with one or more substituents, for example one or more C₁₋₅ alkyl or C₁₋₅ alkoxy groups.

Particularly preferred are triphenylphospine and tris(ortho-methoxytriphenyl) phospine.

The polymerisation reaction may take place in a single organic liquid phase in which all components of the reaction mixture are soluble. The reaction may take place in a two-phase aqueous-organic system, in which case a phase transfer agent may be used. The reaction may take place in an emulsion formed by mixing a two-phase aqueous-organic system with an emulsifier.

The polymer may be end-capped by addition of an endcapping reactant. Suitable end-capping reactants are aromatic or heteroaromatic materials substituted with only one leaving group. The end-capping reactants may include reactants substituted with a halogen for reaction with a boronic acid or boronic ester group at a polymer chain end, and reactants substituted with a boronic acid or boronic ester for reaction with a halogen at a polymer chain end. Exemplary end-capping reactants are halobenzenes, for example bromobenzene, and phenylboronic acid. End-capping reactants may be added during or at the end of the polymerisation reaction.

Non-conjugating Repeat Units

Ar¹ of formula (II) is preferably an aryl group, more preferably phenylene. Phenylene groups Ar¹ may be 1,2- , 1,3- or 1,4-linked phenylene, preferably 1,4-linked phenylene.

Sp of formula (II) may contain a single non-conjugating atom only between the two groups Ar¹, or Sp may contain non-conjugating chain of at least 2 atoms separating the two groups Ar¹.

A non-conjugating atom may be, for example, —CR⁴ ₂— or —SiR⁴ ₂— wherein R⁴ in each occurrence is H or a substituent, optionally a substituent R¹¹ as described above, for example C₁₋₂₀ alkyl.

A spacer chain Sp may contain two or more atoms separating the two groups Ar¹, for example a C₁₋₂₀ alkyl chain wherein one or more non-adjacent C atoms of the chain may be replaced with O, S, —NR₁₁—, —SiR₁₁ ²—, —C(═O)— or —COO—. Preferably, the spacer chain Sp contains at least one sp³-hybridised carbon atom separating the two groups Ar¹.

Preferred groups Sp are selected from C₁₋₂₀ alkyl wherein one or more non-adjacent C atoms are replaced with O. An oligo-ether chain, for example a chain of formula —O(CH₂CH₂O)_(n)— may be provided, wherein n is from 1-5.

Repeat units of formula (II) may be provided in an amount in the range of 1-50 mol %, optionally 20-50 mol %. The polymer may contain two or more different repeat units of formula (II).

Exemplary repeat units of formula (II) include the following:

Arylene Units

The polymer may contain arylene or heteroarylene repeat units, each of which may be unsubstituted or substituted with one or more substituents, and charge-transporting repeat units containing aromatic or heteroaromatic groups.

Exemplary arylene co-repeat units include arylene repeat units, for example 1,2-, 1,3- and 1,4-phenylene repeat units, 3,6- and 2,7-linked fluorene repeat units, indenofluorene, naphthalene, anthracene and phenanthrene repeat units, and stilbene repeat units, each of which may be unsubstituted or substituted with one or more substitutents, for example one or more C₁₋₃₀ hydrocarbyl substituents.

One preferred class of arylene repeat units is phenylene repeat units, such as phenylene repeat units of formula (VI):

wherein q in each occurrence is independently 0, 1, 2, 3 or 4 , optionally 1 or 2; n is 1, 2 or 3; and R³ independently in each occurrence is a substituent.

Where present, each R³ may independently be selected from the group consisting of:

-   -   alkyl, optionally C₁₋₂₀ alkyl, wherein one or more non-adjacent         C atoms may be replaced with optionally substituted aryl or         heteroaryl, O, S, substituted N, C═O or —COO—, and one or more H         atoms may be replaced with F;     -   aryl and heteroaryl groups that may be unsubstituted or         substituted with one or more substituents, preferably phenyl         substituted with one or more C₁₋₂₀ alkyl groups;     -   a linear or branched chain of aryl or heteroaryl groups, each of         which groups may independently be substituted, for example a         group of formula —(Ar³)_(r) wherein each Ar³ is independently an         aryl or heteroaryl group and r is at least 2 , preferably a         branched or linear chain of phenyl groups each of which may be         unsubstituted or substituted with one or more C₁₋₂₀ alkyl         groups; and     -   a crosslinkable-group, for example a group comprising a double         bond such and a vinyl or acrylate group, or a benzocyclobutane         group.

In the case where R³ comprises an aryl or heteroaryl group, or a linear or branched chain of aryl or heteroaryl groups, the or each aryl or heteroaryl group may be substituted with one or more substituents R⁷ selected from the group consisting of:

-   -   alkyl, for example C₁₋₂₀ alkyl, wherein one or more non-adjacent         C atoms may be replaced with O, S, substituted N, C═O and —COO—         and one or more H atoms of the alkyl group may be replaced with         F;     -   NR⁹ ₂, OR⁹, SR⁹, SiR⁹ ₃ and     -   fluorine, nitro and cyano;         wherein each R⁹ is independently selected from the group         consisting of alkyl, preferably C₁₋₂₀ alkyl; and aryl or         heteroaryl, preferably phenyl, optionally substituted with one         or more C₁₋₂₀ alkyl groups.

Substituted N, where present, may be —NR⁹— wherein R⁹ is as described above.

Preferably, each R³, where present, is independently selected from C₁₋₄₀ hydrocarbyl, and is more preferably selected from C₁₋₂₀ alkyl; unusubstituted phenyl; phenyl substituted with one or more C₁₋₂₀ alkyl groups; a linear or branched chain of phenyl groups, wherein each phenyl may be unsubstituted or substituted with one or more substituents; and a crosslinkable group.

If n is 1 then exemplary repeat units of formula (VI) include the following:

A particularly preferred repeat unit of formula (VI) has formula (VIa):

Substituents R³ of formula (VIa) are adjacent to linking positions of the repeat unit, which may cause steric hindrance between the repeat unit of formula (VIa) and adjacent repeat units, resulting in the repeat unit of formula (VIa) twisting out of plane relative to one or both adjacent repeat units.

Exemplary repeat units where n is 2 or 3 include the following:

A preferred repeat unit has formula (VIb):

The two R³ groups of formula (VIb) may cause steric hindrance between the phenyl rings they are bound to, resulting in twisting of the two phenyl rings relative to one another.

A further class of arylene repeat units are optionally substituted fluorene repeat units, such as repeat units of formula (VII):

wherein R³ in each occurrence is the same or different and is a substituent as described with reference to formula (VI), and wherein the two groups R³ may be linked to form a ring; R⁸ is a substituent; and d is 0, 1, 2 or 3.

The aromatic carbon atoms of the fluorene repeat unit may be unsubstituted, or may be substituted with one or more substituents R⁸. Exemplary substituents R⁸ are alkyl, for example C₁₋₂₀ alkyl, wherein one or more non-adjacent C atoms may be replaced with O, S, NH or substituted N, C═O and —COO—, optionally substituted aryl, optionally substituted heteroaryl, alkoxy, alkylthio, fluorine, cyano and arylalkyl. Particularly preferred substituents include C₁₋₂₀ alkyl and substituted or unsubstituted aryl, for example phenyl. Optional substituents for the aryl include one or more C₁₋₂₀ alkyl groups.

Substituted N, where present, may be —NR⁵— wherein R⁵ is C₁₋₂₀ alkyl; unsubstituted phenyl; or phenyl substituted with one or more C₁₋₂₀ alkyl groups.

The extent of conjugation of repeat units of formula (VII) to aryl or heteroaryl groups of adjacent repeat units may be controlled by (a) linking the repeat unit through the 3- and/or 6-positions to limit the extent of conjugation across the repeat unit, and/or (b) substituting the repeat unit with one or more substituents R⁸ in or more positions adjacent to the linking positions in order to create a twist with the adjacent repeat unit or units, for example a 2,7-linked fluorene carrying a C₁₋₂₀ alkyl substituent in one or both of the 3- and 6-positions.

The repeat unit of formula (VII) may be an optionally substituted 2,7-linked repeat unit of formula (VIIa):

Optionally, the repeat unit of formula (VIIa) is not substituted in a position adjacent to the 2- or 7-position. Linkage through the 2- and 7-positions and absence of substituents adjacent to these linking positions provides a repeat unit that is capable of providing a relatively high degree of conjugation across the repeat unit.

The repeat unit of formula (VII) may be an optionally substituted 3,6-linked repeat unit of formula (VIIb)

The extent of conjugation across a repeat unit of formula (VIIb) may be relatively low as compared to a repeat unit of formula (VIIa).

Another exemplary arylene repeat unit has formula (VIII):

wherein R³, R⁸ and d are as described with reference to formula (VI) and (VII) above. Any of the R³ groups may be linked to any other of the R³ groups to form a ring. The ring so formed may be unsubstituted or may be substituted with one or more substituents, optionally one or more C₁₋₂₀ alkyl groups.

Repeat units of formula (VIII) may have formula (VIIIa) or (VIIIb):

Further arylene co-repeat units include: phenanthrene repeat units; naphthalene repeat units; anthracene repeat units; and perylene repeat units. Each of these arylene repeat units may be linked to adjacent repeat units through any two of the aromatic carbon atoms of these units. Specific exemplary linkages include 9,10-anthracene; 2,6-anthracene; 1,4-naphthalene; 2,6-naphthalene; 2,7-phenanthrene; and 2,5-perylene. Each of these repeat units may be substituted or unsubstituted, for example substituted with one or more C₁₋₄₀hydrocarbyl groups.

The polymer may contain one or more hole transporting repeat units. Exemplary hole transporting repeat units may be repeat units of materials having a electron affinity of 2.9 eV or lower and an ionisation potential of 5.8 eV or lower, preferably 5.7 eV or lower.

Preferred hole-transporting repeat units are (hetero)arylamine repeat units, including repeat units of formula (IX):

wherein Ar⁸ and Ar⁹ in each occurrence are independently selected from substituted or unsubstituted aryl or heteroaryl, g is greater than or equal to 1 , preferably 1 or 2 , R¹³ is H or a substituent, preferably a substituent, and c and d are each independently 1, 2 or 3.

R¹³, which may be the same or different in each occurrence when g>1 , is preferably selected from the group consisting of alkyl, for example C₁₋₂₀ alkyl, Ar¹⁰, a branched or linear chain of Ar¹⁰ groups, or a crosslinkable unit that is bound directly to the N atom of formula (IX) or spaced apart therefrom by a spacer group, wherein Ar¹⁰ in each occurrence is independently optionally substituted aryl or heteroaryl. Exemplary spacer groups are C₁₋₂₀ alkyl, phenyl and phenyl-C₁₋₂₀ alkyl.

Any of Ar⁸, Ar⁹ and, if present, Ar¹⁰ in the repeat unit of Formula (IX) may be linked by a direct bond or a divalent linking atom or group to another of Ar⁸, Ar⁹ and Ar¹⁰. Preferred divalent linking atoms and groups include O, S; substituted N; and substituted C.

Any of Ar⁸, Ar⁹ and, if present, Ar¹⁰ may be substituted with one or more substituents. Exemplary substituents are substituents R¹⁰, wherein each R¹⁰ may independently be selected from the group consisting of:

-   -   substituted or unsubstituted alkyl, optionally C₁₋₂₀ alkyl,         wherein one or more non-adjacent C atoms may be replaced with         optionally substituted aryl or heteroaryl, O, S, substituted N,         C═O or —COO— and one or more H atoms may be replaced with F; and     -   a crosslinkable group attached directly to the fluorene unit or         spaced apart therefrom by a spacer group, for example a group         comprising a double bond such and a vinyl or acrylate group, or         a benzocyclobutane group

Preferred repeat units of formula (IX) have formulae 1-3:

In one preferred arrangement, R¹³ is Ar¹⁰ and each of Ar⁸, Ar⁹ and Ar¹⁰ are independently and optionally substituted with one or more C₁₋₂₀ alkyl groups. Ar⁸, Ar⁹ and Ar¹⁰ are preferably phenyl.

In another preferred arrangement, the central Ar⁹ group of formula (IX) linked to two N atoms is a polycyclic aromatic that may be unsubstituted or substituted with one or more substituents R¹⁰. Exemplary polycyclic aromatic groups are naphthalene, perylene, anthracene and fluorene.

In another preferred arrangement, Ar⁸ and Ar⁹ are phenyl, each of which may be substituted with one or more C₁₋₂₀ alkyl groups, and R¹³ is —(Ar¹⁰)_(r) wherein r is at least 2 and wherein the group —(Ar¹⁰)_(r) forms a linear or branched chain of aromatic or heteroaromatic groups, for example 3,5-diphenylbenzene wherein each phenyl may be substituted with one or more C₁₋₂₀ alkyl groups.In another preferred arrangement, c, d and g are each 1 and Ar⁸ and Ar⁹ are phenyl linked by an oxygen atom to form a phenoxazine ring.

Amine repeat units may be provided in a molar amount in the range of about 0.5 mol % up to about 50 mol %, optionally about 1-25 mol %, optionally about 1-10 mol %.

The polymer may contain one, two or more different repeat units of formula (IX).

Amine repeat units may provide hole-transporting and/or light-emitting functionality. Preferred light-emitting amine repeat units include a blue light-emitting repeat unit of formula (IXa) and a green light-emitting repeat unit formula (IXb):

R¹³ of formula (IXa) is preferably a hydrocarbyl, preferably C₁₋₂₀ alkyl, phenyl that is unsubstituted or substituted with one or more C₁₋₂₀ alkyl groups, or a branched or linear chain of phenyl groups wherein each said phenyl group is unsubstituted or substituted with one or more C₁₋₂₀ alkyl groups.

The repeat unit of formula (IXb) may be unsubstituted or one or more of the rings of the repeat unit of formula (IXb) may be substituted with one or more substituents R¹⁵, preferably one or more C₁₋₂₀ alkyl groups.

Light-emitting Layers

A light-emitting layer of an OLED may be unpatterned, or may be patterned to form discrete pixels. Each pixel may be further divided into subpixels. The light-emitting layer may contain a single light-emitting material, for example for a monochrome display or other monochrome device, or may contain materials emitting different colours, in particular red, green and blue light-emitting materials for a full-colour display.

A light-emitting layer may contain a mixture of more than one light-emitting material, for example a mixture of light-emitting materials that together provide white light emission.

A white-emitting OLED may contain a single, white-emitting layer or may contain two or more layers that emit different colours which, in combination, produce white light. White light may be produced from a combination of red, green and blue light-emitting materials provided in a single light-emitting layer distributed within two or more light-emitting layers. In a preferred arrangement, the device has a light-emitting layer comprising a red light-emitting material and a light-emitting layer comprising green and blue light-emitting materials.

The light emitted from a white-emitting OLED may have CIE x coordinate equivalent to that emitted by a black body at a temperature in the range of 2500-9000K and a CIE y coordinate within 0.05 or 0.025 of the CIE y coordinate of said light emitted by a black body, optionally a CIE x coordinate equivalent to that emitted by a black body at a temperature in the range of 2700-4500K.

Exemplary phosphorescent light-emitting materials include metal complexes comprising substituted or unsubstituted complexes of formula (X): ML¹ _(q)L² _(r)L³ _(s)   (X) wherein M is a metal; each of L¹, L² and L³ is a coordinating group; q is an integer; r and s are each independently 0 or an integer; and the sum of (a·q)+(b·r)+(c·s) is equal to the number of coordination sites available on M, wherein a is the number of coordination sites on L¹, b is the number of coordination sites on L² and c is the number of coordination sites on L³.

Heavy elements M induce strong spin-orbit coupling to allow rapid intersystem crossing and emission from triplet or higher states. Suitable heavy metals M include d-block metals, in particular those in rows 2 and 3 i.e. elements 39 to 48 and 72 to 80 , in particular ruthenium, rhodium, palladium, rhenium, osmium, iridium, platinum and gold. Iridium is particularly preferred.

Exemplary ligands L¹, L² and L³ include carbon or nitrogen donors such as porphyrin or bidentate ligands of formula (XI):

wherein Ar⁵ and Ar⁶ may be the same or different and are independently selected from substituted or unsubstituted aryl or heteroaryl; X¹ and Y¹ may be the same or different and are independently selected from carbon or nitrogen; and Ar⁵ and Ar⁶ may be fused together. Ligands wherein X¹ is carbon and Y¹ is nitrogen are preferred, in particular ligands in which Ar⁵ is a single ring or fused heteroaromatic of N and C atoms only, for example pyridyl or isoquinoline, and Ar⁶ is a single ring or fused aromatic, for example phenyl or naphthyl.

To achieve red emission, Ar⁵ are selected from phenyl, fluorene, naphthyl. Ar⁶ are selected from quinoline, isoquinoline, thiophene, benzothiophene.

To achieve green emission, Ar⁵ are selected from phenyl or fluorene. Ar⁶ are selected from pyridine.

To achieve blue emission, Ar⁵ are selected from phenyl. Ar⁶ are selected from imidazole, triazole, tetrazole.

Examples of bidentate ligands are illustrated below:

Each of Ar⁵ and Ar⁶ may carry one or more substituents. Two or more of these substituents may be linked to form a ring, for example an aromatic ring.

Other ligands suitable for use with d-block elements include diketonates, in particular acetylacetonate (acac); triarylphosphines and pyridine, each of which may be substituted.

Exemplary substituents include groups R¹³ as described above with reference to Formula (IX). Particularly preferred substituents include fluorine or trifluoromethyl which may be used to blue-shift the emission of the complex, for example as disclosed in WO 02/45466 , WO 02/44189 , US 2002-117662 and US 2002-182441; alkyl or alkoxy groups, for example C₁₋₂₀ alkyl or alkoxy, which may be as disclosed in JP 2002-324679; carbazole which may be used to assist hole transport to the complex when used as an emissive material, for example as disclosed in WO 02/81448; and dendrons which may be used to obtain or enhance solution processability of the metal complex, for example as disclosed in WO 02/66552.

A light-emitting dendrimer typically comprises a light-emitting core bound to one or more dendrons, wherein each dendron comprises a branching point and two or more dendritic branches. Preferably, the dendron is at least partially conjugated, and at least one of the branching points and dendritic branches comprises an aryl or heteroaryl group, for example a phenyl group. In one arrangement, the branching point group and the branching groups are all phenyl, and each phenyl may independently be substituted with one or more substituents, for example alkyl or alkoxy.

A dendron may have optionally substituted formula (XII)

wherein BP represents a branching point for attachment to a core and G₁ represents first generation branching groups.

The dendron may be a first, second, third or higher generation dendron. G₁ may be substituted with two or more second generation branching groups G₂, and so on, as in optionally substituted formula (XIIa):

wherein u is 0 or 1; v is 0 if u is 0 or may be 0 or 1 if u is 1; BP represents a branching point for attachment to a core and G₁, G₂ and G₃ represent first, second and third generation dendron branching groups. In one preferred embodiment, each of BP and G₁, G₂ . . . G_(n) is phenyl, and each phenyl BP, G₁, G₂ . . . G_(n−1) is a 3,5-linked phenyl.

A preferred dendron is a substituted or unsubstituted dendron of formula (XIIb):

wherein * represents an attachment point of the dendron to a core.

BP and/or any group G may be substituted with one or more substituents, for example one or more C₁₋₂₀ alkyl or alkoxy groups.

Phosphorescent light-emitting materials may be provided in a light-emitting layer with a host material. The host material may be a host polymer of the invention.

The phosphorescent light-emitting material may be physically mixed with the host polymer or may be covalently bound thereto. The phosphorescent light-emitting material may be provided in a side-chain, main chain or end-group of the polymer. Where the phosphorescent material is provided in a polymer side-chain, the phosphorescent material may be directly bound to the backbone of the polymer or spaced apart there from by a spacer group, for example a C₁₋₂₀ alkyl spacer group in which one or more non-adjacent C atoms may be replaced by O or S. It will therefore be appreciated that a composition of the present invention may consist of or may comprise a polymer of the invention comprising repeat units of formula (I) with a phosphorescent light-emitting material bound to the polymer.

In the case where one or more phosphorescent light-emitting materials are mixed with a host material, the phosphorescent light-emitting material(s) may make up about 0.05 wt % up to about 50 wt % of a host/phosphorescent light-emitting material composition.

In the case where one or more phosphorescent light-emitting materials are bound to a host material, for example a host polymer, the phosphorescent light-emitting material(s) may make up about 0.01-50 mol % of the material.

If more than two phosphorescent materials of different colours are used with a single host material then the emitter with the highest triplet energy level may be provided in a greater amount than the other emitter or emitters, for example in an amount of at least two times or at least 5 times the weight percentage of each of the other emitter or emitters.

Charge Transporting and Charge Blocking Layers

In the case of an OLED, a hole transporting layer may be provided between the anode and the light-emitting layer or layers. Likewise, an electron transporting layer may be provided between the cathode and the light-emitting layer or layers.

Similarly, an electron blocking layer may be provided between the anode and the light-emitting layer and a hole blocking layer may be provided between the cathode and the light-emitting layer. Transporting and blocking layers may be used in combination. Depending on its HOMO and LUMO levels, a single layer may both transport one of holes and electrons and block the other of holes and electrons.

A charge-transporting layer or charge-blocking layer may be cross-linked, particularly if a layer overlying that charge-transporting or charge-blocking layer is deposited from a solution. The crosslinkable group used for this crosslinking may be a crosslinkable group comprising a reactive double bond such and a vinyl or acrylate group, or a benzocyclobutane group.

If present, a hole transporting layer located between the anode and the light-emitting layers preferably has a HOMO level of less than or equal to 5.5 eV, more preferably around 4.8-5.5 eV or 5.1-5.3 eV as measured by cyclic voltammetry. The HOMO level of the hole transport layer may be selected so as to be within 0.2 eV, optionally within 0.1 eV, of an adjacent layer (such as a light-emitting layer) in order to provide a small barrier to hole transport between these layers.

If present, an electron transporting layer located between the light-emitting layers and cathode preferably has a LUMO level of around 2.5-3.5 eV as measured by cyclic voltammetry. For example, a layer of a silicon monoxide or silicon dioxide or other thin dielectric layer having thickness in the range of 0.2-2 nm may be provided between the light-emitting layer nearest the cathode and the cathode. HOMO and LUMO levels may be measured using cyclic voltammetry.

A hole transporting layer may contain a homopolymer or copolymer comprising a repeat unit of formula (IX) as described above, for example a copolymer comprising one or more amine repeat units of formula (IX) and one or more arylene repeat units, for example one or more arylene repeat units selected from formulae (VI), (VII) and (VIII).

An electron transporting layer may contain a polymer comprising a chain of optionally substituted arylene repeat units, such as a chain of fluorene repeat units.

If a hole- or electron-transporting layer is adjacent a light-emitting layer containing a phosphorescent material then the T₁ energy level of the material or materials of that layer are preferably higher than that of the phosphorescent emitter in the adjacent light-emitting layer.

Hole Injection Layers

A conductive hole injection layer, which may be formed from a conductive organic or inorganic material, may be provided between the anode 101 and the light-emitting layer 103 of an OLED as illustrated in FIG. 1 to assist hole injection from the anode into the layer or layers of semiconducting polymer. Examples of doped organic hole injection materials include optionally substituted, doped poly(ethylene dioxythiophene) (PEDT), in particular PEDT doped with a charge-balancing polyacid such as polystyrene sulfonate (PSS) as disclosed in EP 0901176 and EP 0947123 , polyacrylic acid or a fluorinated sulfonic acid, for example Nafion®; polyaniline as disclosed in U.S. Pat. No. 5,723,873 and U.S. Pat. No. 5,798,170; and optionally substituted polythiophene or poly(thienothiophene). Examples of conductive inorganic materials include transition metal oxides such as VOx MoOx and RuOx as disclosed in Journal of Physics D: Applied Physics (1996), 29(11), 2750-2753.

Cathode

The cathode 105 is selected from materials that have a workfunction allowing injection of electrons into the light-emitting layer of the OLED. Other factors influence the selection of the cathode such as the possibility of adverse interactions between the cathode and the light-emitting material. The cathode may consist of a single material such as a layer of aluminium. Alternatively, it may comprise a plurality of conductive materials such as metals, for example a bilayer of a low workfunction material and a high workfunction material such as calcium and aluminium, for exampleas disclosed in WO 98/10621 . The cathode may comprise elemental barium, for example as disclosed in WO 98/57381, Appl. Phys. Lett. 2002, 81(4), 634 and WO 02/84759 . The cathode may comprise a thin layer of metal compound, in particular an oxide or fluoride of an alkali or alkali earth metal, between the organic layers of the device and one or more conductive cathode layers to assist electron injection, for example lithium fluoride as disclosed in WO 00/48258; barium fluoride as disclosed in Appl. Phys. Lett. 2001, 79(5), 2001; and barium oxide. In order to provide efficient injection of electrons into the device, the cathode preferably has a workfunction of less than 3.5 eV, more preferably less than 3.2 eV, most preferably less than 3 eV. Work functions of metals can be found in, for example, Michaelson, J. Appl. Phys. 48(11), 4729, 1977.

The cathode may be opaque or transparent. Transparent cathodes are particularly advantageous for active matrix devices because emission through a transparent anode in such devices is at least partially blocked by drive circuitry located underneath the emissive pixels. A transparent cathode comprises a layer of an electron injecting material that is sufficiently thin to be transparent. Typically, the lateral conductivity of this layer will be low as a result of its thinness. In this case, the layer of electron injecting material is used in combination with a thicker layer of transparent conducting material such as indium tin oxide.

It will be appreciated that a transparent cathode device need not have a transparent anode (unless, of course, a fully transparent device is desired), and so the transparent anode used for bottom-emitting devices may be replaced or supplemented with a layer of reflective material such as a layer of aluminium. Examples of transparent cathode devices are disclosed in, for example, GB 2348316.

Encapsulation

Organic optoelectronic devices tend to be sensitive to moisture and oxygen. Accordingly, the substrate preferably has good barrier properties for prevention of ingress of moisture and oxygen into the device. The substrate is commonly glass, however alternative substrates may be used, in particular where flexibility of the device is desirable. For example, the substrate may comprise one or more plastic layers, for example a substrate of alternating plastic and dielectric barrier layers or a laminate of thin glass and plastic.

The device may be encapsulated with an encapsulant (not shown) to prevent ingress of moisture and oxygen. Suitable encapsulants include a sheet of glass, films having suitable barrier properties such as silicon dioxide, silicon monoxide, silicon nitride or alternating stacks of polymer and dielectric or an airtight container. In the case of a transparent cathode device, a transparent encapsulating layer such as silicon monoxide or silicon dioxide may be deposited to micron levels of thickness, although in one preferred embodiment the thickness of such a layer is in the range of 20-300 nm. A getter material for absorption of any atmospheric moisture and/or oxygen that may permeate through the substrate or encapsulant may be disposed between the substrate and the encapsulant.

Formulation Processing

A formulation suitable for forming a charge-transporting or light-emitting layer may be formed from the composition or the polymer of the invention, any further components of the layer such as light-emitting dopants, and one or more suitable solvents.

The formulation may be a solution of the composition or the polymer and any other components in the one or more solvents, or may be a dispersion in the one or more solvents in which one or more components are not dissolved. Preferably, the formulation is a solution.

Solvents suitable for dissolving semiconducting polymers, particularly polymers comprising alkyl substituents, include benzenes substituted with one or more C₁₋₁₀ alkyl or C₁₋₁₀ alkoxy groups, for example toluene, xylenes and methylanisoles.

Particularly preferred solution deposition techniques including printing and coating techniques such spin-coating and inkjet printing.

Spin-coating is particularly suitable for devices wherein patterning of the light-emitting layer is unnecessary—for example for lighting applications or simple monochrome segmented displays.

Inkjet printing is particularly suitable for high information content displays, in particular full colour displays. A device may be inkjet printed by providing a patterned layer over the first electrode and defining wells for printing of one colour (in the case of a monochrome device) or multiple colours (in the case of a multicolour, in particular full colour device). The patterned layer is typically a layer of photoresist that is patterned to define wells as described in, for example, EP 0880303.

As an alternative to wells, the ink may be printed into channels defined within a patterned layer. In particular, the photoresist may be patterned to form channels which, unlike wells, extend over a plurality of pixels and which may be closed or open at the channel ends.

Other solution deposition techniques include dip-coating, roll printing and screen printing.

EXAMPLES Monomer Example 1

Synthesis of Monomer Example 1

A 1 L 3 neck flask fitted with condenser, N₂ inlet/bubbler and overhead stirrer was charged with 2,4-bis(3-bromophenyl)-6-chloro-1,3,5-triazine (15 g, 35 mmol), 3,5-bis(4-tert-octylphenyl)-4-methylbenzene boronic acid pinacol ester (7 g, 12 mmol), toluene (400 mL) and ethanol (133 mL). The slurry was degassed with nitrogen for 1 h before a degassed aqueous solution of potassium carbonate (3.6 g in 133 mL) was added. Degassing continued for 5 mins before tetrakis triphenylphosphine (0.52 g, 0.45 mmol) was added and the mixture was heated to 38° C. (oil bath temp). After 96 h LCMS indicated the product was forming and a further 7 g of the pinacol boronic ester in 50 mL degassed toluene was added followed by a further 3.6 g base (as a solid) and a further 0.52 g of catalyst. The reaction was monitored by HPLC and further portions of pinacol boronic ester, base and catalsyst were added and the temperature was increased to 50° C. (oil bath temp) until the reaction did not progress further. The reaction was cooled to r.t., the layers were separated and the aqueous phase was extracted with toluene (2×100 mL). The combined organic phases were washed with water, dried with magnesium sulphate, filtered and concentrated to yield a yellow oil. The oil was columned using a Biotage Isolera LS flash column system on silica eluting with 15-35% ethyl acetate in hexanes (v/v) and then 10-23% DCM in hexanes (v/v). The product-containing fractions were combined and recrystallised from toluene/IPA to give the product as a white powder (6.91 g, 23%). HPLC indicated a purity of 99.98%.

1H NMR (referenced to CDCl3 peak at 7.26 ppm): 8.83 (2H, s), 8.66 (2H, d), 8.58 (2H, s), 7.72 (2H, d), 7.51 (4H, d), 7.43 (2H, t), 7.38 (4H, d), 2.16 (3H, s), 1.81 (4H, s), 1.47 (12H, s), 0.78 (18H, s)

Monomer Example 2

Synthesis of Monomer Example 2

A 1 L 3 neck flask fitted with condenser, N₂ inlet/bubbler and overhead stirrer was charged with 2,4-bis(3-bromophenyl)-6-chloro-1,3,5-triazine (20 g, 47 mmol), 3-(4-hexylphenyl)benzene boronic acid pinacol ester (5.7 g, 15.8 mmol), toluene (400 mL) and ethanol (133 mL). The slurry was degassed with nitrogen for 1 h before a degassed aqueous solution of potassium carbonate (5 g in 133 mL) was added. Degassing continued for 5 mins before tetrakis triphenylphosphine (0.7 g, 0.6 mmol) was added and the mixture was heated to 36° C. (oil bath temp). After 48 h GCMS indicated the product was forming and a further 5.7 g of the pinacol boronic ester in 60 mL degassed toluene was added and the oil bath temperature was increased to 38° C. The reaction was monitored by GCMS and the oil bath temperature was increased to 50° C. When there was >90% conversion to product as indicated by GCMS the reaction was cooled to r.t. The layers were separated and the aqueous phase was extracted with toluene (2×100 mL). The combined organic phases were washed with water, dried with magnesium sulphate, filtered and concentrated to yield a yellow oil. The oil was columned using a Biotage Isolera LS flash column system on silica eluting with 10-40% DCM in hexanes (v/v). The product-containing fractions were combined and recrystallised from toluene/IPA to give the product as a white powder (11.5 g, 59%). HPLC indicated a purity of 99.8%.

1H NMR (referenced to CDCl3 peak at 7.26 ppm): 8.91 (1H, s), 8.90 (2H, s), 8.68 (3H, d), 7.80 (1H, d), 7.73 (2H, d), 7.61-7.65 (3H, m), 7.45 (2H, t), 7.33 (2H, d), 2.70 (2H, t), 1.67-1.71 (2H, m), 1.33-1.41 (6H, m), 0.91 (3H, t).

Monomer Example 3

Synthesis of Monomer Example 3

A 1 L 3 neck flask fitted with condenser, N₂ inlet/bubbler and overhead stirrer was charged with 2,4-bis(3-bromophenyl)-6-chloro-1,3,5-triazine (15 g, 35 mmol), 3,5-bis(4-tert-octylphenyl)-4-methylbenzene boronic acid pinacol ester (7 g, 12 mmol), toluene (400 mL) and ethanol (133 mL). The slurry was degassed with nitrogen for 1 h before a degassed aqueous solution of potassium carbonate (3.6 g in 133 mL) was added. Degassing continued for 5 mins before tetrakis triphenylphosphine (0.52 g, 0.45 mmol) was added and the mixture was heated to 38° C. (oil bath temp). After 96 h LCMS indicated the product was forming and a further 7 g of the pinacol boronic ester in 50 mL degassed toluene was added followed by a further 3.6 g base (as a solid) and a further 0.52 g of catalyst. The reaction was monitored by HPLC and further portions of pinacol boronic ester, base and catalsyst were added and the temperature was increased to 50° C. (oil bath temp) until the reaction did not progress further. The reaction was cooled to r.t., the layers were separated and the aqueous phase was extracted with toluene (2×100 mL). The combined organic phases were washed with water, dried with magnesium sulphate, filtered and concentrated to yield a yellow oil. The oil was columned using a Biotage Isolera LS flash column system on silica eluting with 15-35% ethyl acetate in hexanes (v/v) and then 10-23% DCM in hexanes (v/v). The product-containing fractions were combined and recrystallised from toluene/IPA to give the product as a white powder (6.91 g, 23%). HPLC indicated a purity of 99.98%.

1H NMR (referenced to CDCl3 peak at 7.26 ppm): 8.83 (2H, s), 8.66 (2H, d), 8.58 (2H, s), 7.72 (2H, d), 7.51 (4H, d), 7.43 (2H, t), 7.38 (4H, d), 2.16 (3H, s), 1.81 (4H, s), 1.47 (12H, s), 0.78 (18H, s)

Polymer Examples

Polymers were prepared by Suzuki polymerisation as described in WO 00/53656 of monomers illustrated below in the amounts shown in Table 1.

TABLE 1 Diester Dibromo monomers monomers Polymer (mol %) (mol %) Mz Mw Mp Mn Pd Comparative A (50) B (5), 404,000 207,000 245,000 17,500 11.82 Polymer 1 Comparative monomer 1 (45) Polymer A (50) B (5), 229,000 105,000 142,000 10,000 11.07 Example 1 Monomer Example 1 (45) Polymer C (50) B (15), 639,000 310,000 381,000 13,000 23.15 Example 2 Monomer Example 1 (35) Polymer A (50) B (25) 342,000 161,000 242,000 6,500 24.91 Example 3 Monomer Example 1 (25) Polymer A (50) B (25.5) 270,000 124,000 173,000 6,900 17.90 Example 4 Monomer Example 2 (24.5) Polymer A (50) B (16) 370,000 180,000 240,000 12,000 14.30 Example 5 Monomer Example 3 (34)

Molar percentages of Monomer Examples 1, 2 and 3 in Polymer Examples 3-5 were adjusted to provide a constant weight percentage of the repeat units derived from these monomers.

It will be appreciated that the extent of conjugation of Polymer Example 2 is greater than that of Polymer Example 1 , which contains a conjugation-breaking repeat unit derived from Monomer A.

Composition Examples

A composition comprising the Polymer Example 1 , the Polymer Example 2 or the Comparative Polymer 1 as described above and 5 wt % of Blue Phosphorescent Emitter 1 , illustrated below, was dissolved in o-xylene for casting as a film by spin-coating.

Blue Phosphorescent Emitter 1

The core of Blue Phosphorescent Emitter 1 is disclosed in WO2004/101707 . Formation of dendrons is described in WO 02/066552.

Synthesis of Blue Phosphorescent Emitter 1

Stage 1:

fac-Tris(1-methyl-5-phenyl-3-propyl-[1,2,4]triazolyl)iridium-

(III)(1.1 g) (Shih-Chun Lo et al., Chem. Mater. 2006, 18, 5119-5129) (1.1 g) was dissolved in DCM (100 mL) under a flow of nitrogen. N-Bromosuccinimide (0.93 g) was added as a solid and the mixture was stirred at room temperature with protection from light. After 24 h HPLC analysis showed ˜94% product and ˜6% dibromide intermediate. A further 50 mg of NBS was added and stirring continued for 16 hours. A further 50 mg of NBS was added and stirring continued for 24 h. HPLC indicated over 99% product. Warm water was added and stirred for 0.5 h. The layers were separated and the organic layer passed through a plug of celite eluting with DCM. The filtrate was concentrated to ˜15 mL and hexane was added to the DCM solution to precipitate the product as a yellow solid in 80% yield.

Stage 2:

Stage 1 material (8.50 g) and 3,5-bis(4-tert-butylphenyl)phenyl-1-boronic acid pinacol ester (15.50 g) were dissolved in toluene (230 mL). The solution was purged with nitrogen for 1 h before 2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl (66 mg) and tris(dibenzylidene)dipalladium (75 mg) were added using 10 mL of nitrogen-purged toluene. A 20wt % solution of tetraethylammonium hydroxide in water (60 mL) was added in one portion and the mixture as stirred for 20 h with the heating bath set to 105° C. T.L.C. analysis indicated all the stage material had been consumed and only one fluorescent spot was observed. The reaction mixture was cooled and filtered into a separating funnel. The layers were separated and the aqueous layer extracted with toluene. The organic extracts were washed with water, dried with magnesium sulphate, filtered and concentrated to yield the crude product as a yellow/orange solid. Pure compound was obtained by column chromatography eluting with a gradient of ethyl acetate in hexanes followed by precipitation from DCM/methanol. HPLC indicated a purity of 99.75% and a yield of 80% (11.32 g)

1H NMR (referenced to CDCl3): 7.83 (3H, d), 7.76 (6H, s), 7.73 (3H, s) 7.63 (12H, d) 7.49 (12H, d), 7.21 (3H, dd), 6.88 (3H, d), 4.28 (9H, s), 2.25 (3H, m), 1.98 (3H, m), 1.4-1.5 (57H, m), 1.23 (3H, m), 0.74 (9H, t).

Properties of films of compositions described above are shown in Table 2 . The photoluminescent quantum yield (PLQY) of the films are comparable for compositions containing Polymer Example 1 and Polymer Example 2 , whereas the PLQY values of the composition containing Comparative Polymer 1 is much lower. Without wishing to be bound by any theory, it is believed that the para-linked triphenyltriazine in Comparative Polymer 1 provides more extended conjugation of the polymer backbone, which results in a lower triplet energy level and quenching of the phosphorescence, compared to increased triplet levels of the polymers of the invention provided by the meta-linked triphenyltriazine. Polymer Example 1 has a lowest triplet excited state energy (T₁) value as measured by time resolved photoluminescence spectroscopy of 2.76 eV, whereas the T₁ value for Comparative Polymer 1 is 2.60 eV.

TABLE 2 Polymer PLQY (%) CIE x CIE y Polymer Example 1 80 0.159 0.295 Polymer Example 2 83 0.157 0.293 Comparative 66 0.160 0.310 Polymer 1

Device Examples 1 and 2

Organic light-emitting devices having the following structure were prepared:

ITO (147 nm)/HIL (34 nm)/HTL (22 nm)/LE/Cathode,

wherein ITO is an indium-tin oxide anode; HIL is a hole-injecting layer; HTL is a hole-transporting layer; LE is a light-emitting layer comprising the host polymer of the invention and a blue phosphorescent dopant; and the cathode comprises a layer of metal fluoride in contact with the light-emitting layer and a layer of aluminium formed over the layer of metal fluoride.

Devices containing Polymer Examples 1 and 2 as host polymer show approximately double the half life (time taken for brightness to fall to 50% of an initial value at constant current) and similar conductivity to devices containing of Comparative Polymer 1 as a host polymer.

Surprisingly, it was found that the conductivity is not affected by the increased triplet levels of the polymers of the invention. Voltage of Device Example 1 containing Polymer Example 1 at a current density of 10 mA/cm2 was 5.91 V and was 5.99 V for Comparative Device 1 containing Comparative Polymer 1.

Device Examples 3-5

Organic light-emitting devices having the following structure were prepared:

ITO (147 nm)/HIL (34 nm)/HTL (22 nm)/LE/Cathode,

wherein ITO is an indium-tin oxide anode; HIL is a hole-injecting layer; HTL is red light emitting hole-transporting layer; LE is a light-emitting layer comprising the host polymer of the invention; and the cathode comprises a layer of metal fluoride in contact with the light-emitting layer and a layer of aluminium formed over the layer of metal fluoride.

A glass substrate carrying ITO was cleaned with UV/Ozone treatment and a layer of a conductive polymer available from Plextronics Inc was formed by spin-coating.

A hole-transporting layer was formed by spin-coating Hole-Transporting Polymer 1 followed by crosslinking of the polymer.

A light-emitting layer was formed by spin-coating Formulation containing a host polymer, Blue Phosphorescent Emitter 2 and Green Phosphorescent Emitter 1 as set out in Table 3.

TABLE 3 Blue Green Device Phosphorescent Phosphorescent Example Host (wt %) Emitter 2 (wt %) Emitter 1 (wt %) 3A Polymer Example 3 35 1 (64) 3B Polymer Example 3 40 1 (59) 4A Polymer Example 4 35 1 (64) 4B Polymer Example 4 40 1 (59) 5A Polymer Example 5 35 1 (64) 5B Polymer Example 5 40 1 (59)

Blue Phosphorescent Emitter 2

Green Phosphorescent Emitter 1

Hole-Transporting Polymer 1 was formed by Suzuki polymerisation as described in WO 00/53656 of the following monomers:

Device performance is set out in Tables 4-6 . Polymers 4 and 5 containing repeat units with bulky substituents derived from Monomers 2 and 3 respectively produce higher efficiency (Table 5) and lower drive voltage and LT70 (Table 6) than Polymer 3 containing repeat units derived from Monomer 1 . LT70 is the time taken for luminance to decay to 70% of an initial value at constant current.

TABLE 4 Efficiency Device CIE (x) CIE (y) (lm/W) CCT (K) CRI DUV 3A 0.40 0.43 331.20 3758.87 73.90 0.02 4A 0.44 0.43 329.20 3067.67 73.50 0.009 5A 0.42 0.42 325.10 3342.76 73.80 0.010 3B 0.41 0.40 308.00 3314.07 68.90 0.00 4B 0.44 0.41 319.90 2988.02 71.90 0.005 5B 0.419 0.41 315.4 3320.55 72.1 0.006

TABLE 5 V J V Lm/W Cd/A EQE at 1 at 1 at 10 Eff. Eff. at 1 Max De- kcd/m² kcd/m² ma/cm² at 1 at 1 kcd/m² EQE vice (V) (mA/cm²) (V) kcd/m² kcd/m² (%) (%) 3A 4.95 3.80 5.83 16.91 26.62 11.53 12.27 3B 4.6 3.60 5.46 19.11 28 12.51 12.86 4A 4.51 3.50 5.22 19.69 28.35 12.68 13.07 4B 4.85 4.70 5.56 13.65 21.2 9.97 11.03 5A 4.5 4.00 5.29 17.61 25.26 11.51 12.08 5B 4.5 3.60 532 19.32 27.77 12.82 13.22

TABLE 6 LT70 J Luminance dV at Device (hours) (mA/cm²) (cd/m²) T70 3A 20.594 3.29 1000.0 0.39 4A 30 3.12 1000.0 0.40 5A 34.385 3.08 1000.00 0.39 3B 15.342 4.24 1000.0 0.48 4B 22.149 3.50 1000.0 0.35 5B 35.4 3.14 1000.00 0.39

Photostability

An improvement in photo stability has also been achieved with the polymers of the invention, as shown in FIG. 2. The photo stability of binary blends of host polymer (64 wt %) and Blue Phosphorescent Emitter 1 (36 wt %) was measured as described below: Samples were fabricated by depositing the blend directly onto a glass substrate using the method described above to form a film approximately 75 nm in thickness. The films were then encapsulated under an inert atmosphere. The samples were photo-excited with 405 nm light using a diode laser and the resultant emission detected at normal incidence using a fibre-coupled spectrometer. The intensity of the exciting beam was varied between samples such that the initial flux of emitted light was approximately equal. The time taken for the emission to drop to 70% of its starting value was then measured. Without wishing to be bound by any theory, it is believed that the improved stability of the polymers of the invention stems from decreased back-transfer of triplets from the emitter to the host polymer due, to their increased triplet levels.

Although the present invention has been described in terms of specific exemplary embodiments, it will be appreciated that various modifications, alterations and/or combinations of features disclosed herein will be apparent to those skilled in the art without departing from the scope of the invention as set forth in the following claims. 

The invention claimed is:
 1. A composition comprising a polymer and a phosphorescent material wherein the polymer comprises repeat units of formula (III):

wherein: R¹ in each occurrence is independently C₁₋₄₀hydrocarbyl, —OR¹¹, —SR¹¹, —NR¹¹ ₂, or —SiR¹¹ ₃; R¹¹ each occurrence is C₁₋₄₀hydrocarbyl; R² is a C₁₋₄₀hydrocarbyl; and n is 0, 1, 2, 3 or
 4. 2. The composition according to claim 1, wherein the polymer comprises one or more co-repeat units.
 3. The composition according to claim 2, wherein the polymer comprises an arylene co-repeat unit that may be unsubstituted or substituted with one or more substituents.
 4. The composition according to claim 2, wherein the one or more co-repeat units include a conjugation-breaking repeat unit that does not provide any conjugation path between repeat units adjacent to the conjugation-breaking repeat unit.
 5. The composition according to claim 4, comprising one or more co-repeat units of formula (II):

wherein: Ar¹ in each occurrence independently represent an aryl or heteroaryl group that may be unsubstituted or substituted with one or more substituents; and Sp represents a spacer group comprising at least one carbon or silicon atom.
 6. The composition according to claim 1, wherein the phosphorescent material is mixed with the polymer.
 7. The composition according to claim 1, wherein the phosphorescent material is covalently bound to the polymer.
 8. The composition according to claim 1, wherein the phosphorescent material has a photoluminescent spectrum with a peak in the range of 420-490 nm.
 9. A formulation comprising the composition according to claim 1 and at least one solvent.
 10. An organic light-emitting device comprising an anode, a cathode and a light-emitting layer between the anode and cathode wherein the light-emitting layer comprises the composition according to claim
 1. 11. A polymer comprising a repeat unit of formula (III):

wherein: R² is a C₁₋₄₀hydrocarbyl; R¹ in each occurrence is independently C₁₋₄₀hydrocarbyl, —OR¹¹, —SR¹¹, —NR¹¹ ₂, or —SiR¹¹ ₃; R¹¹ each occurrence is C₁₋₄₀hydrocarbyl; and n is 0, 1, 2, 3 or
 4. 12. The composition of claim 1, wherein the polymer further comprises a repeat unit of formula:

wherein q is 0, 1, 2, 3 or 4 and R³ independently in each occurrence is selected from the group consisting of: alkyl, wherein one or more non-adjacent C atoms may be replaced with optionally substituted aryl or heteroaryl, O, S, substituted N, C═O or —COO—, and one or more H atoms may be replaced with F; aryl or heteroaryl groups that may be unsubstituted or substituted with one or more C₁₋₂₀ alkyl groups; a group of formula —(Ar³)_(r) wherein each Ar³ is independently an aryl or heteroaryl group and r is at least 2, wherein each Ar³ may be unsubstituted or substituted with one or more C₁₋₂₀alkyl groups; and a crosslinkable-group.
 13. The composition according to claim 1, wherein the polymer does not comprise a fluorene repeat unit.
 14. The polymer according to claim 11, wherein R² is an aromatic ring or a branched or linear chain of aromatic rings, wherein each ring may be unsubstituted or substituted with one or more substituents R⁴, wherein each R⁴ is independently a C₁₋₂₀alkyl, wherein one or more non-adjacent C atoms of the C₁₋₂₀alkyl may be replaces with O or S, and one or more H atoms of the C₁₋₂₀alkyl may be replaced with F.
 15. The polymer according to claim 11, wherein the polymer further comprises a repeat unit of formula (IX):

wherein; Ar⁸ and Ar⁹ in each occurrence are independently selected from subsutitited or unsubstituted aryl or heteroaryl; g is greater than or equal to 1; R¹³ is H or a substituent ; and c and d are each independently 1, 2 or
 3. 16. The polymer of claim 11, wherein the polymer further comprises a repeat unit of formula

wherein q is 0, 1, 2, 3 or 4 and R³ independently in each occurrence is selected from the group consisting of: alkyl, wherein one or more non-adjacent C atoms may be replaced with optionally substituted aryl or heteroaryl, O, S, substituted N, C═O or —COO—, and one or more H atoms may be replaced with F; aryl or heteroaryl groups that may be unsubstituted or substituted with one or more C₁₋₂₀alkyl groups; a group of formula —(Ar³)_(r) wherein each Ar³ is independently an aryl or heteroaryl group and r is at least 2, wherein each Ar³ may be unsubstituted or substituted with one or more C₁₋₂₀alkyl groups; and a crosslinkable-group.
 17. The polymer according to claim 11, wherein the polymer does not comprise a fluorene repeat unit.
 18. A method of forming a polymer comprising the step of polymerising a monomer of formula (IV):

wherein LG is a leaving group capable of leaving in a coupling reaction to form a carbon-carbon bond with an aromatic or heteroaromatic group, and wherein R¹, R² and n are as defined in claim
 1. 19. The method according to claim 18, wherein each LG is independently selected from the group consisting of halogens, boronic acids; boronic esters; sulfonic acids; and sulfonic esters.
 20. The method according to claim 19, wherein the polymerization is carried out in the presence of a metal catalyst. 